在 Object 类中，不考虑重写的情况
内存地址
- 对象在内存中的位置，每个对象都是不同的
- 在java中内存中的对象地址是可变的（例如在内存回收的过程中内存地址就有可能发生变化）
hashcode
内存地址通过哈希计算得出的一个数值，不同对象有可能相同
equals
Object 内部是通过 == 实现，也就是说比较的是内存地址
如何获取到对象的内存地址
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public static Method getArrayBaseOffsetMethod() {
try {
Method method = Class.forName("sun.misc.Unsafe").getDeclaredMethod("arrayBaseOffset", Class.class);
method.setAccessible(true);
return method;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
public static Method getAddressSizeMethod() {
try {
Method method = Class.forName("sun.misc.Unsafe").getDeclaredMethod("addressSize");
method.setAccessible(true);
return method;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
public static Method getIntMethod() {
try {
Method method = Class.forName("sun.misc.Unsafe").getDeclaredMethod("getInt", Object.class, long.class);
method.setAccessible(true);
return method;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
public static Method getLongMethod() {
try {
Method method = Class.forName("sun.misc.Unsafe").getDeclaredMethod("getLong", Object.class, long.class);
method.setAccessible(true);
return method;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
public static long addressOf(Object o) throws Exception {
Field field = Class.forName("sun.misc.Unsafe").getDeclaredField("theUnsafe");
field.setAccessible(true);
Object unsafeObject = field.get(null);
Object[] array = new Object[]{o};
int baseOffset = (int) getArrayBaseOffsetMethod().invoke(unsafeObject, Object[].class);
int addressSize = (int) getAddressSizeMethod().invoke(unsafeObject);
long objectAddress;
switch (addressSize) {
case 4:
objectAddress = (int) getIntMethod().invoke(unsafeObject, array, baseOffset);
break;
case 8:
objectAddress = (long) getLongMethod().invoke(unsafeObject, array, baseOffset);
break;
default:
throw new Error("unsupported address size: " + addressSize);
}
return (objectAddress);
}
